(a) Field of the Invention
The present invention relates to a fuel cell vehicle. More particularly, the present invention relates to an emergency start device of a fuel cell vehicle emergency starts when a direct current-direct current (DC/DC) converter fails in the fuel cell vehicle that has a high voltage battery.
(b) Description of the Related Art
A fuel cell system that is applied to a hydrogen fuel cell vehicle, which is one of environment-friendly future vehicles includes a fuel cell stack that generates electrical energy with an electrochemical reaction of a reaction gas, a hydrogen supply device that supplies hydrogen, which is fuel to the fuel cell stack, an air supply device that supplies air including oxygen, which is an oxidizing agent necessary for an electrochemical reaction to the fuel cell stack, a heat and water management system that controls an operation temperature of the fuel cell stack by discharging heat, which is a by-product of an electrochemical reaction of the fuel cell stack to the exterior and that performs a water management function, and a fuel cell system controller that operates the fuel cell system.
In a vehicle in which such a fuel cell system is mounted, when using only a fuel cell as a power source, the fuel cell provides a charge of the loads of constituent elements constituting the vehicle and thus in an operating area in which efficiency of the fuel cell decreases, performance may deteriorate. Further, when a sudden load is applied to the vehicle, power may not be fully supplied to a driving motor and thus a performance of the vehicle may deteriorate due to electricity generated by a chemical reaction. In addition, since the fuel cell has one direction output characteristics, when no separate power storage means exists, when the vehicle brakes, energy injected from a driving motor may not be recovered and thus efficiency of a vehicle system may deteriorate.
Therefore, as a method of supplementing the drawbacks, a fuel cell hybrid vehicle has been developed. The fuel cell hybrid vehicle is a system that mounts a power storage means, for example, a super capacitor (e.g., super cap) or a high voltage battery that can be charged and discharged as a separate auxiliary power source for providing power necessary for driving a load, such as a driving motor in addition to a fuel cell, which is a major power source in a larger vehicle such as a bus as well as a smaller vehicle such as a sedan.
In a fuel cell-battery hybrid vehicle, a fuel cell that is used as a major power source and a high voltage battery that is used as an auxiliary power source are coupled in parallel, and such a high voltage battery (e.g., main battery) and a low voltage battery (e.g., 12V auxiliary battery) for driving low voltage driving parts of the vehicle are mounted, i.e., a high voltage battery and a low voltage battery, which are two kinds of batteries are mounted together.
When starting a fuel cell, hydrogen and air should be supplied to the fuel cell, and until the fuel cell reaches a normal operating state, since high voltage driving parts (e.g., an air blower) may not be driven with an output of the fuel cell, in a state that supplies hydrogen from a hydrogen tank to the fuel cell by opening a hydrogen supply valve (e.g., starting/stop), by driving an air supply device, (e.g., an air blower with power of a high voltage battery) air including oxygen that is used as an oxidizing agent should be supplied to the fuel cell. The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.